FIG. 15 is a schematic view illustrating a configuration of a power conditioner 100 including an inverter 10 which performs an interconnection output to a power system P.
As illustrated in FIG. 15, the power conditioner 100 including the inverter (also referred to as a “system interconnection inverter”) 10 is known, and the inverter 10 converts a high DC voltage, which is acquired by a DC/DC converter 20 boosting a low DC voltage output from a solar battery S or the like, into an AC voltage and performs an interconnection output to a commercial power system P (for example, refer to Patent Literature 1 or Patent Literature 2).
Incidentally, in the power system P, problems such as an instantaneous voltage rise, an instantaneous voltage drop, a sudden phase change, and an instantaneous power failure may occur.
FIG. 16 is a table showing conditions for a sudden phase change test. FIG. 17 is a schematic view illustrating a configuration of the inverter (Heric) 10 subjected to the sudden phase change test. FIG. 18 is a waveform chart showing an example of a result of the sudden phase change test.
As illustrated in FIG. 18, when a sudden phase change occurs in a system voltage Vac of the power system P, an overcurrent is generated from the power system P side toward the inverter 10. In this example, an output coil current I, which is normally maintained at approximately 40 A, reaches −350 A (since the current is an alternating current, the sign changes depending on the direction of the current). The inverter 10 has a configuration in which such a rapid change on the power system P side is absorbed by output coils L1 and L2 (serving as cushions) provided on the output side of the inverter 10 so that damage to the device is avoided.
A protective circuit, although it is not applied to the inverter described above, for protecting a PWM control device from an overcurrent without stopping an operation of the PWM control device when an overcurrent is generated in the PWM control device has been is proposed (for example, refer to Patent Literature 3).